Magnetron with helical cathode held by support, the output and mode suppression means being remote from the cathode support



NOV. 29, 1966 ADlKEs ET AL 3,289,023

MAGNETRON WITH HEDICAL CATHODE HELD BY SUPPORT. THE OUTPUT AND MODE SUPPRESSION MEANS BEING Filed April 30, 1963 REMOTE FROM THE CATHODE SUPPORT 2 Sheets-$heet 1 INVENTORS. WILLIAM L. Aomss BY KENNETH MSP/TZER NOV. 29, 1966 w ADlKEs ET AL 3,289,023

MAGNETRON WITH HELICAL CATHODE HELD BY SUPPORT, THE OUTPUT AND MODE SUPPRESSION MEANS BEING REMOTE FROM THE CATHODE SUPPORT Filed April 30, 1963 2 Sheets-Sheet 2 INVENTORS. WILL MM LAD/K55 BY KENNETH V. SP/TZEP AGENI United States Patent O MAGNETRON WITH HELICAL CATHODE HELD BY SUPPORT, THE OUTPUT AND MODE SUP- PRESSION MEANS BEING REMOTE FROM THE CATHODE SUPPORT William L. Adikes, Huntington, and Kenneth V. Sprtzer, North Babylon, N.Y., assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Apr. 30, 1963, Ser. No. 276,838 2 Claims. (Cl. 315-3953) Our invention relates to a magnetron, and more particularly, to a fixed frequency magnetron having reduced coupling of R-F power to the cathode and a higher output efiiciency.

In a magnetron, an axially mounted cathode structure can couple in an infinite number of ways to a circular series of cavities forming a slow wave structure around it. If this slow wave structure is completely symmetrical, most of these coupling mechanisms cancel. In a normal crossed-field microwave oscillator slow wave structure, the major deviations from this symmetry result from the circular dissymmetry, the output, and the axial dissymmetries, for example, mode suppressing straps. These dissymmetries produce coupling most strongly in their immediate vicinity. If, for example, the straps are at the axial extremes of the slow Wave structure, coupling fields do not strongly penetrate the electron interaction region.

It is a principal object of our invention to provide a magnetron having reduced undesired coupling between the slow wave structure and the cathode.

A further object of our invention is to provide a magnetron having greatly increased output efiiciency.

A still further object of our invention is to provide a magnetron of simplified structure which is adapted to be coupled directly to either a coaxial line output or a wave-guide output.

Another object of our invention is to provide a method of simplifying the assembly of a magnetron of greatly increased output efiiciency.

These and other objects of our invention will appear as the specification progresses.

In accordance with the invention, we have found that by placing all mode suppressing straps and the output coupling at one axial extreme of the slow wave structure, and by introducing a cathode from the opposite axial extreme of the slow wave structure, limiting the projection of this cathode beyond the structure into the strap output coupling region, the coupling of the slow wave structure to the cathode is greatly decreased. Consequently, the efiiciency of the device when coupled to either a coaxial line or a wave-guide is greatly increased.

The slight amount of coupling found still to exist due to the fact that some part of the cathode must still be in the vicinity of the strap output coupling field has little effect on the output efficiency, for the coaxial line formed by the cathode as a center lead and the slow wave structure as the outer lead does not readily propagate in the axial direction.

We have also found that a directly-heated filamentary type cathode can be employed quite successfully in this construction and gives efiiciencies comparable to a cylindrical cathode in a c-w magnetron. We prefer, however, to employ a helical cathode whose pitch is at least 1.5 times the wire diameter, and preferably between 2.0 and 100 times the diameter.

Another feature of the magnetron, according to the invention, is the provision of a novel output coupling which enables the output to be coupled directly to either a coaxial line, to a wave-guide, or to a closed cavity.

In this case, the output system is constructed to give the connector for the center conductor of the R-F coaxial line on the tube side of the coupling, a configuration, so that when it is inserted to a depth predetermined by the configuration of the outer conductor into a wave-guide, at a proper distance from a short-circuit in the waveguide, it also serves as a narrow band, matched coupling to the wave-guide.

The invention both as to its construction and operation will be described in connection with the accompanying drawing in which:

FIG. 1 is a sectional view of the magnetron according to the invention;

FIG. 2 is a sectional view of a portion of the slow wave structure showing the strap coupling;

FIG. 3 is a sectional view of the output coupling; and

FIG.4 is a plan view of the section 1VIV in FIG. 3.

As shown in FIG. 1 of the drawing, the magnetron, according to the invention, comprises an enclosure 1 into which a tubular cathode support 2 extends. A helical cathode 3, comprising a plurality of turns of thoriated tungsten wire having a diameter of about 1 mm., is supported by the end 4 of the cathode support. The upper end of the cathode is secured to a rod 6 which is one conductor supplying current to the cathode which is directly heated, the other conductor being the outer tubular supporting member 2. The turns of the cathode have a pitch which is 2.5 times the diameter of the wire. Outer conductor 2 is separted from the metal enclosure 1 by an insulator 7.

Plates 5 serve as end plates to deflect stray electrons which otherwise might enter the end space and not contribute to the generation of R-F power.

An anode block, generally designated 8, has a central aperture 9, extending axially the entire length of the block through which the cathode 3 extends. On the side of the anode block remote from the end of cathode support 2 is a magnetic pole system 10 for producing a magnetic field which extends through the block. The cathode 3, as can be seen from the drawing, extends beyond the anode block 8, a distance not exceeding 25% of the anode length in the axial direction.

Extending outwardly from the anode block 8, on the side remote from the tubular cathode support 2, is an output system generally designated 11 which will be described in greater detail, infra.

The anode block comprises an annular member 12 (see FIG. 4) from which a plurality of partitions, or vanes v13, extend inwardly, the inner edges of which define the central aperture 9 in which cathode 3 is located. Radial partitions 13 define between them a plurality of cavities 14 which are resonant at a particular frequency determined by the dimensions of the cavity, as is wellknown to those skilled in this art. In accordance with one aspect of the invention, these partitions preferably have a length in the axial direction which is less than the radial dimension of the partitions.

Since circular dissymmetries in cavities introduce spunous modes of pair of conductive straps 16 and 17 which interconnect alternate vanes 13, placed at the end of the anode block 8 eifectively suppress undesired oscillations.

hese straps are conveniently placed in notches 18 proided in the vanes.

A further novel feature of the magnetron, according a the invention, is the output coupling which permits a lirect connection to either a coaxial conductor system, a vave-guide, or closed cavity. The outer tubular conluctor 19 connected to the enclosure terminates at an )utput cup 20 through washers 21 and 22. Inner conluctor 23 terminates in a cup 24 which can serve as an antenna for a wave-guide coupling. A conical insulator 25 serves to space cup 20 from cup 25, and provides a racuum seal.

While we have described our invention in connection with a specific embodiment, other modifications thereof will be apparent to those skilled in this art without departing from the spirit and scope of the invention.

What we claim is:

1 An electron discharge device comprising an enclosure, a cathode support extending into said enclosure, a slow-wave structure within said enclosure and comprising an annular anode block having a plurality of resonant cavities opening into a central aperture in the anode block, magnetic field producing means Within said enclosure and spaced from the end of said anode block remote from the cathode support, a helical cathode mounted on said cathode support extending into and coaxial with the central aperture of the anode block, said helical cathode being coextensive with and extending beyond the anode a distance not exceeding about 25% of the anode length in the axial direction, mod'e suppressing straps interconnecting the resonant cavities of the anode block only on the side thereof remote from the cathode support, and means to couple said resonant cavities to an output system disposed on the side of the anode block remote from the cathode support, said coupling means comprising an inner conductor element havconductor element for connecting the same to an outer conductor of a coaxial conductor system, and a coaxial insulating member connecting said flange to the open end of said cup-shaped portion of the inner conductor element for fixedly positioning the same within said outer conductor element whereby the output of the device may be connected to a coaxial conductor system or a waveguide.

2. An electron discharge device as claimed in claim 1 in which the cathode comprises a plurality of wire turns having a pitch-at least 1.5 times the diameter of the wire.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES I. R. G. Twisleton, Twenty-kilowatt 890 mc./s. Continuous-Wave Magnetron, Proc. IEE, vol. 111, No. 1, January 1964, pages 51-56 relied on.

HERMAN KARL SAALBACH, Primary Examiner.

R. D. COHN, Assistant Examiner. 

1. AN ELECTRON DISCHARGE DEVICE COMPRISING AN ENCLOSURE, A CATHODE SUPPORT EXTENDING INTO SAID ENCLOSURE, A SLOW-WAVE STRUCTURE WITHIN SAID ENCLOSURE AND COMPRISING AN ANNULAR ANODE BLOCK HAVING A PLURALITY OF RESONANT CAVITIES OPENING INTO A CENTRAL APERTURE IN THE ANODE BLOCK, MAGNETIC FIELD PRODUCING MEANS WITHIN SAID ENCLOSURE AND SPACED FROM THE END OF SAID ANODE BLOCK REMOTE FROM THE CATHODE SUPPORT, A HELICAL CATHODE MOUNTED ON SAID CATHODE SUPPORT EXTENDING INTO AND COAXIAL WITH THE CENTRAL APERTURE OF THE ANODE BLOCK, SAID HELICAL CATHODE BEING COEXTENSIVE WITH AND EXTENDING BEYOND THE ANODE A DISTANCE NOT EXCEEDING ABOUT 25% OF THE ANODE LENGTH OF THE AXIAL DIRECTION, MODE SUPPRESSING STRAPS INTERCONNECTING THE RESONANT CAVITIES OF THE ANODE BLOCK ONLY ON THE SIDE THEREOF REMOTE FROM THE CATHODE SUPPORT, AND MEANS TO COUPLE SAID RESONANT CAVITIES TO AN OUTPUT SYSTEM DISPOSED ON THE SIDE OF THE ANODE BLOCK REMOTE FROM THE CATHODE SUPPORT, SAID COUPLING MEANS COMPRISING AN INNER CONDUCTOR ELEMENT HAV- 